Process for the reduction of fine iron ores



Feb. 8, 1938. H. scHMALr-'ELDT PROCESSFOR THE-REDUCTION 0F FINE IRONCRES 2 Sheets-SinaaiI l Filed Dec. ll, 19.54

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Feb. 8, 1938. H. scHMALx-'ELDT PROCESS FOR THE REDUCTION OF FINE IRO'NORES Filed Dec. 11, 1934 2`Sheets-Sheet 2 INVENT Patented Feb. 8, 1938PATENT "OFFICE PROCESS FOR THE REDUCTION .OF FINE IRON ORES Hanss'chmalfelat, Cassel-Bundaberg, Germany Application December y11, 1934,Serial No. 756,968

y In Germany December 12, 1933 9 Claims.

\ This invention relates to a process for the reduction of fine ironores.

It is well known to reduce iron ores on a commercial scale in blastfurnaces.

All possible processes and apparatus have been proposed for the purposeof undertaking the reduction of pulverized ores to iron powder. Thereduction in a rotating drum through which the reducing gases are passedhas been the only one which has proved practical. Here it is suitable toWork in countercurrent, so that the fresh gases, which act as a reducingagent, cool the reduced ore and on the otherqhand, Vthe used escapinggases preheat the freshly supplied ore. The processes which Vdo not workin rotating drums were not successful because, in the shaft fur'- naceswhich then come into consideration the ore lies nearly or quite stilland thereby sintering or caking takes place. Nopulverized iron,therefore, can be obtained, for mechanical reasons alone, if a drum isnot used. Added to this, the passage for the gas is blocked by thesintering and the ore does not receive a sufficient supply o-f gas.Therefore, Veven in cases Where sintered material is required, a drum isalso to be preferred.

It has now been found that the heavy ore gives rise to relatively littleloss in dust, so that the process can also be carried out in a rotatingreduction drum even with Very fine ores.

While therefore the reduction of ne ores with gases in a rotating drumis in itself possible, it was however found that there couldbe noquestion of its working economically, for the following reasons:

1. The reducinggases can only be utilized to a small extent. Duringthereduction with e. g. carbon monoxide, only about a third of thecarbon monoxide'can be converted, while the remaining two thirds remainunattached; the same is true with hydrogen. In order to obtain asufcient speed of reaction, it is necessary to keep sufficiently remotefrom the equilibrium composition of the gases which lies Within about63-68% CO. The reaction with carbon monoxide, for instance, takes placein accordance with the 55 equation FeO-l-COl-"Fe-l-COz. The reaction isUsually the fur-- nace is charged with lumps of ore and coke, or

reversible and in equilibrium if about 60% of the present gases is CO.In the equilibrium state the reaction works neither from the left sideto the right or vice versa: the equilibrium is obtained. Inv order tostart a reaction from the left to the iight side of the equation which,of course, is desired, it is necessary to use a larger amount of CO,s'ay about 90%. This means that only 90% minus 60% equals 30% CO reallyreduces, whereas the remaining part is lost as far as its heat value isconcerned. The escaping gases which take with them about two thirds ofthe heat value, cannot be used again without further treatment. as thereaction products carbon dioxide and steam oppose further decom-Position. 'A y 2. vThe reduction of iron oresis endothermic, i. e. heatmust be supplied for the reduction. It becomes all the more endothermicwhen this ore is also mixed with finely divided carbon in order to savereducing gas. But it is not only the endothermic reaction of thereduction process itself which absorbs the heat, but there are alsoadditional losses in heat by radiation and conduction in the rotatingdrum and also by the sensible heat in the gases which are escaping andin the completely reduced ores. The reaction heat can naturally besupplied in small units by heating the drum from outside. As however thereduction temperature lies between '750 and 900 C. external heatingalready causes considerable difficulty, even on a laboratory scale, asthe reduction drum becomes red hot thereby. On a large scale the supplyof heatcan no longer be undertaken through the drum, not onlyl on`account of diculties of the material but also because the proportion ofdrum surface to drum content or output becomes increasinglyunfavcurable, it is therefore compulsory to use internal combustion, i.e. it is therefore necessary to in-` troduce airinto the reduction gasduring the process. By this means a portion of the reduction gas isburnt, so that the reaction heat and loss of heat are balanced. Thedirect internal heating is of course bound up with the greatdisadvantage that the reduction capacity of the reduction gas isdiminished as, by the combustion of the air the same reaction endproducts are formed as those which are formed during the reduction ofthe iron, namely carbon dioxide andA steam. l

It has now been found by practical experiments that the weakening of thereduction powerv of the reducing gases can be so great under somecircumstances that a reduction to the required extent does not takeplace. 'This is above all the case when the reduction gases areunsuitable for the reduction. The reduction gases which containmany'hydrocarbons are, rst and foremost, unsuitable, as the hydrocarbonsmust split first into carbon monoinde and'hydrogen, before the reductionprocess by means of carbon monoxide and hydrogen starts. Now thesplitting or' the hydrocarbons is also a Strongly endothermic reaction.

The reaction heat for the reaction must naturally also be produced bythe burning by means of air in the reducing drum. Hereby carbon dioxideand steam which oppose to the further reduction of iron ore, are againobtained as reaction proucts.

The idea now occurs to free the reaction only a third of which has beenused up, water vapeur and carbon dioxide, after it has passed throughthe drum and again to'circulate it. A short consideration however showsthat by gases,

, the continual internal combustion-even in the most favorable case-somuch nitrogen `is introduced that the reduction gases are considerablydiluted by the nitrogen and thereby rendered valueless. Even if theequilibrium cannot be shifted by the dilution with nitrogen, the speedof reaction will, however, be considerably decreased. On the other handthe speeds of the gas 'stream in-the drum arel increased, so that thegas has less time to react with the iron ore. Consequent- 1y the outputis still further diminished and under some circumstances only a fractionof the output which is obtained` when fresh gases are used, can beobtained. 1 I. have found that the previous diiliculties can be avoidedby the new process and apparatus described in the followingspecification and illustrated in the accompanying drawings in which-VFlg. 1 is a diagrammatic view of the apparatus for carrying out theprocess'of the present inventlon; v A,

2 is a sectional elevational view of the reduction-drum shown in Fig. 1;

Y 3 is a transverse sectional View of the drum;

Fig. 4 is. an elevational view of the controi head; Y Fig. 5 is atransverse section of the rotary part of the control head; and

Fig. is'a'transverse section of the stationary part of the control head.

The process .according to the present invention is carried out in thefollowing way:

The reaction heat is not produced by the introduction of air but by theintroduction of pure so that no dilution with nitrogen takes Theescaping gases, only a third vof which 4has been used up, are then freedfrom carbon dioxide and steam and, after being mixed with fresh gases,returned into the 'Ihe washing out takes place bypassing the escapinggases through carbonio acid absorbingliquids, such as solutions ofcaustic soda, or by means of compressing the escaping gasesand washingout the carbonio acid by means of water at low' temperatures of 10 toC., preferably under pressures of 5 tc'30 atmospheres.- According to afurther improvement of the invention such reducing gases are used in thereduction drum which contain either no or practically no hydrocarbons(less than 3%), ln order to save the heat for cracking the hydrocarbons.The new process is therefore characteroxygen, place; i

ized by a combination or' the following features:

1. The use of from as a considerable portion of the residual gases mustalways be removed in order equilibrium of nitrogen in the drum. Even Aifit were desired to return the gases, it would only be possible to returna smali portion and the residue must be given upv as lost. During theprocess'of combustion with pure oxygen, definite quantities of nitrogenare, naturally, introduced with the burning gas. By choosing a suitablecombustion gas, this quantity ofl nitrogen can, however, -be

considerably reduced. If water-gas is used, for instance, then onlyabout 5% of nitrogen is introduced;A with cracked coke furnace gas undersome circumstances even less.

The freeing of the residual vgases from carbon dioxide is preferablycarried out in the following manner: v

The cool residual gases are compressed in a small compresso-r and-passedthrough a water` tower in a known manner with a pressure of about 10-15atmospheres, in which the carbon dioxide is washedout with water. .'I'hesteam formed has already been condensed during the cooling; the lastquantities are condensed withV a large quantity of water during thefurther cooling of the gases by the washing. The gases freed from carbondioxide and steam are again'heated by heat exchange with the hot gasesleaving the drum and are then expanded in an expanding machine for thepurpose of recovering mechanical work.`

The compression and also the expansion can be undertaken in pistonengines aswell as in turbines. Preferably botlr machines are connectedto one shaft. Any suitable power engine desired may provide the energystill necessary. If they are suiciently preheated by the gases comingfrom the drum, itis possible so to arrange to maintain the thecompressed preheated gases give nearly as v much energy as is requiredfor the compression of the cold gases. -The washing water is forced intothe Wash tower in a known manner by means of a high pressure pump andafter leavingthe tower re-expanded by means of a freely radiatingturbine or a Francis turbine, for the recovering of energy. Here also itis best to arrange the pump and turbine together with the motor, whichsupplies the residual energy, on one shaft.

The usual reduction gases come into consideraa tion as reduction gases.Examples for these reduction gases are: distillation gases of mineralcoal, Igas of coke oven, gas obtained by slowly burning carbonaceousmateriai, natural gas, gas from oil cracking plants, gas obtained by thedecomposition of o ll; gases free from hydrocarbons: water gas, 'crackeddistillation gases, such as cracked coke oven gas, i. e. gases in whichthe hydrocarbons have been decomposed.

The oxygen necessary for the internal combustion is produced in theusual manner, for instance, by electrolysis of Water or by decompositionof air.

' out with external heating, in some cases with v Examplesv I. A highper cent iron ore with about 90% FezGs, in so far as it is not nnelygranular, is ground and then placed in the feeding hopper (a) (seeFig. 1) of the reduction drum. The material is fed into the reducingdrum. (b) by a worm or any other feeding device. The ore is ilrst heatedby the escaping gases and then reaches vzones of such high temperaturesthat the reduction' begins. After the reduction has been completed, the

ore is cooled by the cold reduction gases introduced at (c) and thenfalls into a delivery casing, from which it is removed by a worm. Thereduction temperature is obtained by the introduction of oxygen into thereducing drum, according to a preferred form of construction (see below)by means of a large number of nozzles (d) The supply of oxygen to thedrum takes place through a kind of sliding head.

The used reduction gases escape at (e) with temperatures oi' about 250to 500 C., according to the quality of the ore and reach a heatexchanger (f). After cooling'in the heat exchanger and, if necessaryafter a final cooling, the gas is sucked by a compressor (g) andcompressed to a pressure of about 5 to 30 atmospheres, preferably 12atmospheres and forced into the carbon dioxidewashing tower (h) underthis pressure. The gas cooled and freed from` carbon dioxide passesthrough (k) back into the said heat exchanger and reaches, in a warmcondition, a 'pressure reducing machine (l), where the pressure isreduced to atmospheric pressure. The compression and the pressurereducing machines may be both piston machines or also turbines. Thegases freed'from carbon dioxide and steam arrive back in the drumthrough '(c) after that portion of the gases which has been used up bythe reduction and the internal combustion has been replaced through (m)II.-An ore poor in iron is to be reduced with the object later ofseparating, by a magnetic process, the reduced ore from the gangue. Inthis case the process is carried out similarly to I but the heatexchangerlf) `is omitted as the gases will probably emerge too cold tomake heat recovery pay. In this case the emerging gases are thereforeimmediately washed and cooled, they then reach the compressor, arelforced from this into the carbon dioxide-washing chamber, are expandedagain by means of a pressure reducing machine, so that a part of thecompression energy is recovered and then ow back into the drum.

The reduction is carried out at temperatures of ,750 to 900 C.,preferably at temperatures of 800-830" C.

The rotary drum may be lined with any materlal generally used for thelining of furnaces, such as stones of silicate or fire brick. There isno need here to pay much attention to the nature of the gangue of theores as the temperatures in the drum are not high, and there is no needto fear the formation of molten liquids.

It has already been proposed to use gases free from hydrocarbons for thereduction of. iron ores.

'But, on the one hand, these gases were only mentioned as alternativesor by way of example, i. e. it was not recognized that the freedom ofthe reduction gases from hydrocarbons was an essential condition forsuccessful reduction. Besides, in all these previous proposals the othercharacteristics of the newer combination are lacking. In some cases theprocess was carried the use oi air. Moreover the special nature of theregeneration proposed -according to this invention was always lacking.

It is also already known to use, as reduction gases for the reduction ofiron ores, the gases resulting during the obtaining of by-products whichare relatively poor in hydrocarbons; such gases, however, always contain2540% hydrocarbone.

The advantages of the new process relatively to what was known are thefollowing:

The new process can be carried out simply and practically and works witha minimum cost for gas, as owing to the special kind of the process, thegas used is used up completely. With the new process it is possible toproduce iron powder directly. The degree of reduction obtained, amountsto about i. e. 85% of the total iron present isrecovered as metalliciron, the rest as FeO. It is however possible to drive the degree ofreduction still higher.

As deposits may be formed, under some circumstances at those places inthe drum at which the oxygen is introduced, as over-beatings may easilyoccur there and the material begin to cake, it is advisable to removethis disadvantage by providing a number of nozzles forvthe introductionof the oxygen and only to introduce the oxygen by the nozzles inquestion when the nozzles are in their upper positions, so that the ironore or iron being blown on directly by the hot oxygen flame does notcome into question, but the gas only is heated. 'I'he connection, i's,for example, so chosen that the oxygen is only introduced in-that partof the drum which is disposed above the middle plane of the drum. Eachnozzle which is fastened to the periphery of the drum and receives itsoxygen from outside and blows it into the drum, receives the supply ofoxygen during that portion of the revolution which lies above the middleplane. For example, if the revolution is followed from the top pointback to the top point again, the oxygen is supplied on the top point.The introduction of the oxygen still continues while the drum rotatesthrough i. e. until the intersection oi' the path of the nozzle and themiddle plane. Then the addition of oxygen from the nozzle in question isinterrupted during the period of a revolution of 180 and only taken upagain after the second passage through the middle plane.

`This is obtained constructively by connecting thenozzles which lieapproximately in the same line of the jacket, by pipes which connectwith a control head which is fastened onto the drum. The control headprovides for the relevant 'connection.

The advantage obtained by this form of construction is that a directheating of the iron is avoided, and further, that the nozzles'"can coolduring the time in which they are not burning, whereby the heating ofthe nozzles to too high a temperature is avoided. A

It is preferable to arrange the nozzles insuch a way that the emergingoxygen` lies either entirely or partly in an axial direction. l(Theblowing direction of the nozzlesmust not be purely radial but must beslightly inclined in order that the blowing direction receives an axialcomponent. The purpose of this device is to give the flames a longerpath so that they cannot meet the opposing wall so easily.) This avoidssome of the material to be reduced dropping into the nozzles.

, is after the reduction.

Finally according to the invention it is possible to avoid theinconvenient washing out ofl the carbon dioxide from the residual gases,that For this purpose the mixture of carbon monoxide and hydrogen, whichVis to be used for thereduction, is first converted,

as regardsthe carbon monoxide by means of steam at temperatures of380-550, preferably about 425, so that a mixture of hydrogen and carbondioxide results from the conversion. The

, carbon dioxide is then removed in any desired manner, for instance, byputting the gas under pressure of ,530 atmospheres and washing withwater in a known manner at temperatures of l-20 C.. or by means ofcarbonic acid absorbing liquids. The putting under pressure may be alsocarried out previous to the conversion. After the washing a gas isobtained which consists a1- most entirely of hydrogen. The reduction isnow undertaken with this gas whereby the following advantages areobtained.

About a third to two fifths of the gases are used up during thereduction. The gas mixture which leaves the furnace consists therefore,for example, of about 60% hydrogen and 40% steam. Now it is possible towork up the residual gas in a very simple manner, it is only necessaryto cool them, whereby the water vapour is condensed and pure hydrogenremains behind. The gases thus puried, after the oxidized 40% of thehydrogen has been replaced by fresh hydrogen, are then again supplied tothe reduction drum.

Naturally, by this process, it is necessary to wash out the samequantity of carbon dioxide as in the process first described. However inthe altered process the relations are considerably more favourable. Ifthe process is started with a definite quantity of carbonmonoxide-hydrogen mixture, for example one cubic'metre, then three cubicmetres must be led through the reduction i drum if one third of thesegases is always used for the reduction. After the rst process the carbondioxide must be washed out from 3 cubic metres of gas, while accordingto the altered process, it is only necessary to wash out from one cubicmetre of gas. Since now the quantities of water required for washing arein the i'lrst place proportional to the quantities of gas and thequantities of water to beused are likewise proportional to the mentionedoutput of gas i. e.

. the amount of gas passing through the device in one unit of time, sayone minute, so the energy required for washing out the carbon dioxide inthe rst process is about three times as large as it would be with thealtered process. This shows clearly the great advantage of this methodof carrying out the process. KK i 'I'he reduction drum for carrying outthe process, especially. the process with the alternate addition ofoxygen, consists of an iron drum (a, Fig. 2) with a refractory lining q)which is also heatinsulating. 0n the surface of the drum there are pipes(r) which lead the oxygen to the nozzles (s). Several nozzles areconnected with each pipe on the spots where heat is Wanted due to thereduction i. e. where oxygen must be introduced. The number of thenozzles of course depends on the size of the drum, for ordinary sizes anumber of 8, 30 or 50 nozzles will come into consideration. the interiorof the drum not radially, but wholly or partly in axial direction insuch a way, that a somewhat longer 'I'hereby it is avoided that theflames touch the opposite wall.

monoxide and being The nozzles discharge into path of the flames isobtained.A

By means of a control head (v) it is possible to discharge oxygen onlyif thenozzles lie above the middle plane. Therefore the nozzlesindicated in the drawings by are working, whilst the nozzles not markedare not supplied with oxygen. The regulation of the oxygen is carriedout by means of the control-head (o). Each of the pipes (r) dischargesinto this control-head. 'I'he rotary part of the control-head (cut :r-x,Fig. 5) is subdivided in a number of chamberscorresponding to the numberof pipes. Each chamber shows a trapeze-shaped opening in the frontilange, through which the connection with the stationary part (u) of thecontrol head is formed. Oxygen is introduced at (t) into the part (u).The chamber (u), according to the cut Zl-y. (Fig. 6) does not show anysubdivision into cells, but the upper part of the nal ilange is missingin such a way that the oxygen can enter only into these cells of therotating part of the control-head which are just on top.

I claimz- 1. Process for the production of iron powder from fine ironores in a rotary reduction drum comprising the step of bringing intocontact the iron ores with reducing gases comprising carbon monoxide,introducing pure oxygen into the drum, the heat for heating the ores to750 C. to 900 C. being produced by internal combustion of a part of thereducing gases by means of said pure oxygen, the further step ofremoving the combustion products from the discharged reducling gases bycooling the latter to 10 C. to 20 C. and washing the reducing gasesleaving the drum by means of carbon dioxide absorbing liquids, andreconveying the puried gases together With fresh gases to the drum.

2. Process for the production of iron powder from ne iron ores in arotary reduction drum comprising the step of bringing into contact theiron ores with reducing gases comprising carbon monoxide and beingpractically free from hydrocarbons, introducing pure oxygen into thedrum, the heat for heating the ores to 750 C. to 900 C. being producedby internal combustion of a part of the reducing gases by means of saidpure oxygen, the further step of removing the combustion products fromthe discharged reducing gases by cooling the latter to 10 C. to 20` C.and washing "the reducing gases leaving the drum by means of water andreconveying the purified gases together with fresh gases to the drum.

3. Process for the production of iron powder .from Ailne iron ores .in arotary reduction drum comprising the step of bringing into contact theiron ores with reducing gases .comprising carbon practically free fromhydrocarbons, introducing pure oxygen into the drum,

the heat for heating the ores to approximatelyo 815 C. being produced byinternal combustion of -a part of the reducing gases by means of saidpure oxygen, the further step of removing the combustion products fromthe discharged reducing-gases by cooling the latter to approximately 15C. and washing. the reducing gases leaving the drum by 'means of Waterunder a pressure of 5-30 atm. and reconveying the puried gases togetherwith fresh gases to the drum. y

4. Process for the production of iron powder from line iron ores in arotary reduction drum comprising` the step .of bringing into contact theiron ores with reducing galses comprising carbon monoxide and beingpractically fre from hydrocarbons, introducing pure oxygen into thedrum,

the heat for heating the ores to approximately 815 C. being produced byinternal combustion of a part of the reducing gases by means of saidpure oxygen, the further step of removing the combustion products fromthe discharged reducing gases by cooling the latter to approximately 15C. and washing the reducing gases leaving the drum with water after theyhave been compressed to a pressure of -30 atm. heating the purified gasby the waste gases of the drum, expanding-the mentioned purified gasesand reconveying them to the drum.

5. Process for the production of iron powder from fine iron ores in arotary reduction4 drum comprising the step of bringing into contact theiron ores with reducing gases comprising carbon monoxide, introducingpure oxygen into the drum, the heat for heating the ores to '150 C. to900 C. being produced by internal combustion of a part of the reducinggases by means of said pure oxygen, which is added at many pointsalternately in such a way that only an indirect heating of the irontakes place, the further step of removing the combustion products fromthe discharged reducing gases by cooling the latter to C. to 20 C. andwashing the reducing gases leaving the drum by means of carbon dioxideabsorbing liquids and reconveying the purified gases together with freshgases to the drum.

6. Process for the production of iron powder from iine iron ores in arotary reduction drum comprising the step of bringing into contact theiron ores with reducing gases comprising carbon monoxide and beingpractically free from hydrocarbons, introducing pure oxygen into thedrum, the heat for heating the ores to750" C. to 900 C. being producedby internal combustion of a part ofthe reducing gases by meansoi' saidpure oxygen, which is added at many points alternately in such a waythat only an indirect heating of the iron takes place, the further stepof removing the combustion products from the discharged reducing gasesby cooling the latter to 10 C. to 20 C. and washing the reducing gasesleaving the drum by means of carbon dioxide absorbing liquids and 5reconveying the purified gases together with fresh gases to the drum.

7. Process for the production of iron powder from tine iron ores in arotary reduction drum comprising the step of bringing into contact theiron ores with reducing gases comprising carbon monoxide-and beingpractically free from hydrocarbons. introducing pure oxygen into thedrum, the heat for heating the ores to approximately 815 C. beingproduced by internal combustion of a part of the reducing gases by meansof said pure oxygen, which is added at many points aiternately in such away that only an indirect heating of the iron takes place, the .furtherstep of removing the combustion products from the dischargedreducinggases by cooling the latter to approximately C. and washingunder a pressure of 5-30 atm. the reducing gases leaving the drum bymeans of water and reconveying the purified gases together with freshgases to the drum.

8. Process forv the production of iron powder from ne iron ores in arotary reduction drum comprising the step of bringing into contact theiron ores with reducing gases comprising carbon monoxide and beingpractically free from hydrocarbons, introducing pure oxygen into thedrum, the heat for heating the ores to approximately 815 C. beingproduced by internal combustion of a part of the reducing gases by meansof said pure oxygen, which is added at many points alternately in such away that only an indirect heating of the iron takes place, the furtherstep of removing the combustion products from the discharged reducinggases by cooling the latter to approximately 15 C. and washing thereducing gases leaving the drum with water after they have beencompressed, heating the puried gas by the waste gases oi the drum,expanding the mentioned puried gases and reconveying them t9 the drum.

9. Process for the production of iron powder from fine iron ores in arotary reduction drum comprising the step of bringing into contact theiron ores with reducing gases comprising carbon monoxide and beingpractically free from hydrocarbons, introducing pure oxygen into thedrum, the heat for heating the ores to approximately 815 C. beingproduced by internal combustion of a part of the reducing gases by meansof said pure oxygen, which is added at many points alternately in such away that only an indirect heating of the iron takes place, the stream ofoxygen being introduced into the gas room in a substantially axialdirection, the further step of removing the combustion products from thedischarged reducing gases by cooling theV latter to approximately 15 C.and washing the reducing gases leaving the drum with water after theyhave been compressed to 5-30 atm., heating the purified gas by the wastegases of the drum, expanding the mentioned purified gases andreconveying them to the drum.

HANS SCHMALFELDT.

